Linear motion variable resistor



LINEAR MOTION VARIABLE RESISTOR Original Filed April 30. 1953 FIG. 2

w 2 s 26 3 & A\ 3| 5 3| Qi! l5 qr IO/Z I 9 i 1 Lil 57 INVENTORS 4 MARLANE. BOURNS EDWARD J. GOEPPINGER 146EN T 2,998,587 LINEAR MOTION VARIABLERESISTOR Marlan E. Bourns and Edward J. Goeppinger, Riverside,

Calif.; said Goeppinger assignor to Bourns, Inc., a corporation ofCalifornia Original application Apr. 30, 1953, Ser. No. 352,215. Di-

vided and this application Mar. 3, 1958, Ser. No. 718,563

3 Claims. (Cl. 338-183) The present invention relates to variableresistors or otentiometers, and more particularly to that type ofinstrument wherein a contact-carrying member is moved along the lengthof a resistance element by rectilinear or reciprocating movement of anoperating member. This invention is a division of our co-pendingapplication, Serial No. 352,215, filed April 30, 1953, now Patent Number2,857,497 entitled Linear Motion Variable Resistor.

Heretofore, linear motion resistors have usually been made with thecontact-carrying slider fixedly mounted on one end of a reciprocatingoperating rod, and the latter has been slidably supported on theinstrument housing for longitudinal movement. The other end of the rodprojects from the housing and is attached to a movable actuating memberon the device with which the resistor is associated. Movement of thesaid actuating member causes the contact-carrying slider to be shiftedalong the length of the resistance element.

One of the serious disadvantages of this arrangement lies in the factthat the instrument must be precisely aligned with the actuating memberof the associated device; otherwise, misalignment will cause bending ofthe operating rod or binding of the instrument, or will cause excessivewear of the operating rod bearing in the instrument, or of the deviceactuating the instrument. The misalignment problem in conventionallinear motion resistors, as heretofore constructed, is further magnifiedby the fact that the contact-carrying member is rigidly fixed to theoperating rod, and therefore any deflection or bending of the rod underside thrust results in displacement of the contact toward or away fromthe resistance element. The consequence of this is that the contactbears harder against the resistance element at one end thereof than atthe other. The increased pressure at the one end causes increased wearof the contact and element, While the decreased pressure at the otherend of the element tends to make the instrument more susceptible tovibrational error.

The primary object of the present invention, therefore, is to provide alinear motion variable resistor wherein the contact-carrying slider isaccurately guided along a path parallel to the resistance element by aguide means on the housing entirely independent of the operating member,and the latter is connected to the slider by means providing for alimited amount of relative movement of the operator with respect to theslider to accommodate misalignment between the actuating member and theoperator. The principal advantage of this arrangement is that iteliminates the problem of maintaining parallelism and alignment betweenthe operating member and the slider, and insures accurate alignment anduniform pres sure of the contact with respect to the resistance elementat all times.

Another object of the invention is to provide a variable resistor of theclass described, wherein the operating member is connected to the sliderby means providing for a limited amount of relative movement by theoperator with respect to the slider, so as to accommodate ted States Fatlateral displacement of one with respect to the other. This eliminatesside thrust of the operating rod against its bearing, and preventsexcessive bearing wear, binding, and abnormal wear of the contact andresistance element.

A further object of the invention is to provide a linear motion variableresistor wherein the cooperating guide means on the housing and slidermay readily be manufactured to such close tolerances and perfection offit that vibration of the slider with respect to the resistance elementis substantially eliminated, thereby eliminating hash or noise. Hash, ornoise, may be defined as electrical fluctuations in resistor outputresulting from intermittent electrical discontinuities between thecontact and the resistance element, and is a serious problem with linearmotion resistors of conventional design owing to the fact that it ispractically impossible to make the operating rod and its bearing withsuch close tolerances and perfection of fit that the rod will notvibrate within the bearing under conditions encountered in aircraft andmissile use. Such vibration of the operating rod causes the contactassembly, which is attached thereto, to chatter on the resistanceelement and thereby produce the electrical discontinuities referred to.Accuracy and precision of guiding the slider are further enhanced in thepresent invention by slidably supporting the slider immediately adjacentthe point of contact with the resistance element. In prior resistors,the housing slidably supports the operating rod, and there is sometimesa considerable overhang of the rod and attached contact beyond the pointof support.

Another object of the invention is to provide a construction wherein themass of the contact-carrying slider is reduced to the minimum, therebyminimizing inertia for better response, and also minimizing the effectof acceleration.

The foregoing and other objects and advantages of the present inventionwill become apparent to those skilled in the art upon consideration ofthe following description of two preferred embodiments thereof,reference being had to the accompanying drawings, wherein:

FIGURE 1 is a vertical sectional view through a linear motion resistorembodying the principles of our invention, taken at 1-1 in FIGURE 2;

FIGURE 2 is a transverse vertical section through the same instrument,taken at 2-2 in FIGURE 1;

FIGURE 3 is a perspective view of the base member of the instrument; and

FIGURE 4 is a fragmentary sectional view through a modified form of theinvention.

Referring first to FIGURES 1 to 3 of the drawings, the instrument isdesignated inits entirety by the reference numeral 10. The instrument 10is seen to comprise a housing 11, which includes a base member 12, withends 13 and 14, which are enclosed within a tubular sleeve or casing 15.The ends 13, 14 have circumferential grooves 16 formed therein, andseated within these grooves are 0 rings 17, which seal the clearancesbetween the ends and the casing 15. The casing 15 is secured to the endsby screws 18.

The base member 12 is preferably formed of a thermosetting dielectricplastic material, such as phenolic resin, which may be molded, extruded,or machined to the form shown. in cross section, the member 12 has theshape of a segment of a circle; the underneath surface of the memberbeing cylindrically curved, and the top surface being fiat. Twolaterally spaced, parallel grooves 20 and 21 are formed in the fiat, topsurface of the member 12, and seated Within these grooves are acollector strip 22 and wire wound resistance element 23, respectively.Three angular-ly spaced locating holes or cavities 24 are drilled orotherwise formed in the ends of the member 12, and these are engaged byprojections 25 extending inwardly from the faces of the end members 13,14. This arrangement permits the base member 12 and the end members 13,14 to be assembled in accurately located relationship Mounted in andextending between the ends 13, 14 are two laterally spaced guide rods26, which are parallel to the electrical members 22., 23. Slidablysupported on the guide rods 26 is a contact-carrying slider 30. Theslider 30 may be formed, as shown in FIGURE 2, with outwardly facinggrooves or channels 31 formed in opplosite sides thereof, which receivethe guide rods 26. A flat plate 32 of dielectric plastic material ismounted on the bottom side of the slider 30, and attached to the plateis a U. shaped contact member 33, the ends of which wipe on thecollector strip 22 and resistance element 23. The electrical signal isas picked up from the resistance element 23 and transferred over to thecollector strip 22 by the contact member 33, and the latter is insulatedfrom the slider 39 by the dielectric plate 32.

Mounted in the left-hand end member 13 are three angularly spacedconnector pins 34, which are adapted to receive a connector plug. Two ofthe pins 34 are connected to opposite ends of the resistance element 23;while the third pin 34 is connected to the collector strip 2-2. By thismeans, a voltage difference may be applied to the ends of the resistanceelement, and the voltage at any intermediate point engaged by thecontact 33 will be transferred to the third pin.

The slider 30 is accurately guided along a path parallel to theelectrical elements 22, 23 by the guide rods 26. The slider 30 is movedalong the length of the elements 22, 23 by means of an operating member35, which, in FIGURES l to 3, comprises a flexible wire. One end of thewire 35 is inserted into a hole in the end of the slider 30 and issecured therein by a set screw 36. The wire 35 passes through a hole 4%in the right-hand end member 14-, which is sealed against the entranceof dirt by an O ring 41. The O ring 41 is seated within a counterbore42, and is backed up by a tubular retainer 43. The other end of the wire35 is attached to the movable actuating member (not shown) on the devicewith which the instrument is associated, and movement of the saidactuated member is transmitted to the slider 30 to produce an electricalsignal.

The operating member 35, being a flexible wire, provides a flexibleconnection between the actuating member and the slider 30 whicheliminates any problem of misalignment between the two parts. If theinstrument should be misaligned with respect to the actuating member onthe associated device, any non-parallelism in the travel of theactuating member and slider 3G is compensated for by the resilientoperating member 35.

In the embodiment shown in FIGURE 4, the instrument is designated by thereference numeral 1%, and is seen to be generally similar to theconstruction just described. In this form, however, the operating member35' comprises a cylindrical rod, one end of which is reduced in diameterat 45 and extends through a hole 46 in slider 36). The hole 4-6 issomewhat larger than the reduced portion 45 of the operating rod, sothat there is a substantial amount of clearance between them. A hole 50is bored into the end of the slider 3G, leaving a relatively thin wall51, through which the hole 46 extends. By thus reducing the length ofthe hole 46, a substantial amount of looseness can be obtained betweenthe operating rod 35' and the slider 3d.

Wavy spring washers 52 and 53 are interposed between the operating rod35 and the opposite sides of wall portion 51. Spring washer 52 bearsagainst the right-hand side of wall portion 51, and seats against ashoulder 54 at the junction of the reduced neck 45 with the main body ofthe rod 35'. Spring washer 53 bears against the left-hand side of thewall portion 51, and seats against a regular flat washer 55, which isfastened to the reduced neck 45 in any suitable manner. The springwashers 52,

53 permit a limited amount of angular deflection of the rod 35 withrespect to the slider 30, yet at the same time, take up a clearance sothat there is no backlash between them. The connection between theoperating rod 35' and the slider 30 is, in efiect, a universal joint,permitting angular deflection of the rod with respect to the slider.

The operating rod 35 passes through an oversize hole 56 in the endmember 14, and through an O ring 57 of rubber or other elastomericmaterial, which is seated in a circumferential groove 58 in the sides ofthe hole. The 0 ring 57 fits snugly around the operating rod 35' to sealthe interior cavity against the entrance of dirt or moisture. At thesame time, the resilience of the O ring allows a limited amount oflateral displacement of the operating rod so as to accommodatemisalignment between the actuating member to which the rod 35' isconnected, and the slider 30'.

In each of the two embodiments of the invention described, thecontact-carrying slider is accurately guided along a path parallel tothe resistance element and collector strip by guide means on the housingindependent of the operating means. At the same time, the operatingmember is connected to the slider by a flexible form of connection whichaccommodates any misalignment between the instrument and the actuatingdevice with which it is associated.

While we have shown and described in considerable detail what we believeto be the preferred forms of our invention, it will be understood thatvarious changes may be made without departing from the scope of thebroad claims appended hereto.

We claim:

1. A variable resistor comprising an elongated housing having anenclosed cavity provided therein, a rectilinear resistance elementmounted on said housing within said cavity, a slider supported forlinear movement along a path parallel to said resistance element, acontact on said slider wiping on said resistance element, an operatingrod flexibly connected at one end to said slider for a limited amount ofangular deflection with respect thereto, said operating rod extendingfrom one end of said slider parallel to the line of travel thereof andpassing through an oversize hole in one end of said housing, and anannular sealing member of elastomeric material encircling said operatingrod and closing said hole, said annular sealing member being yieldablein the direction perpendicular to the axis of said operating rod so asto accommodate lateral displacement of the latter at the point where theoperating rod passes through the end of said housing.

2. A variable resistor comprising a housing, a rectilinear resistanceelement mounted on said housing, a slider supported for linear movementalong a path parallel to said resistance element, a contact on saidslider wiping on said resistance element, said slider having a holeextending through it in the direction parallel to the line of travel, anoperating rod disposed parallel to the line of travel of said slider andhaving one end extending loosely through said hole, and spring meansbearing against said operating rod and engaging opposite sides of saidslider adjacent the edges of said hole, said spring means permittinglimited angular movement of said operating rod with respect to saidslider while preventing relative movement of the operating rod withrespect to the slider along the direction of travel of the latter.

3. A variable resistor comprising a housing, a rectilinear resistanceelement mounted on said housing, a slider supported for linear movementalong a path parallel to said resistance element, a contact on saidslider wiping on said resistance element, said slider having a roleextending through it in the direction parallel to the line of travel, anoperating rod disposed parallel to the line of travel or" said sliderand having one end extending loosely through said hole, said operatingrod extending through a hole in the end of said housing of largerdiameter than the diameter of the rod, elastomeric sealing meansdisposed within said last-mentioned hole and slid- References Cited inthe file of this patent UNITED STATES PATENTS Newnham May 13, 1952Gottschall June 19, 1956 Gearheart et al. Nov. 12, 1957 Bourns Apr. 22,1958 Bourns Oct. 21, 1958 Gottschall Jan. 26, 1960 UNITED STATES'PATENT. OFFICE CERTIFICATE OF CORRECTION Pate t Nou 2 ,998,587 August29, 1961 Marlan E. Bourns et all:

at error appears in the above numbered pat- It is hereby certified th dLetters Patent should read as ent requiring correction and that the saicorrected below.

Signed and sealed this 3rd day of April 1962.

(SEAL) Attest:

ERNEST W. SWIDEB Attesting Officer DAVID L. LADD Commissioner of PatentsPatent No, 2,998,587

UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION I '7 August 29. 1961 Marlan E. Bourns et a1,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below Column 4 line 43, strike out "of elastomeric material".

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVYID LJLADDI Commissioner ofPatents

